Telephone transmitter



SePt- 11, 1951 H. ECKARDT TELEPHONE TRANSMITTER Filed June 9, 1949 Hll FREQUENCY- CYCLES PER SECO/V0 /NVEA/TOR H. E C KA R07' 4T TORNE Y Patented Sept. 11, 1951 U NTD STAT EVS PATE NT?v OFFl if TELEPHONE TRANSMITTER l Helmuth Eckardt, Towaco, N.'J., assignorf'to BellV Telephone 'Labotre`s, Inorpatd, New York,'N.'Y., a. corporation of New York Application June 9, 1949, Serial No. 97,972

11 claims: (c1. 179-124) This invention relates to telephone transmitters and more particularly to such transmittersof the carbon granule inertia type.

One general object of this invention is to irnprove the performance of carbon `granule -type telephone transmitters.

`-More specific objects of this invention are to vices is extended, to minimize changes in the operating characteristics of such transmitters with variations in ambient pressure or temperature or both, to improve the frequency response characteristic, and to reduce harmonic and modulation product distortion.

In illustrative embodiments of this invention, l

a telephone transmitter comprises, in general, a rigid hollow body or container mounted for vibration in accordance with vsound waves eiective thereon, the body having therein lcomminuted resistance varying material, such as carbon granules, and having also therein an electrode mounted so that relative motion between the electrode and body occurs when the latter is vibrated, whereby the resistance of the current `path through the comminuted material is modulated in accordance with the sound Waves.

In accordance with one feature of this invention, the hollow body is constructed so that the characteristics of the relative motion between the electrode and the body are substantially unaiected by variation in ambient temperature conditions. Specically, in one illustrative embodiment, the body comprises two metallic hemispheres joined in edge-to-edge relation to form an air-tight housing, a diaphragm dividing the interior of the housing into two chambers', carbon granules in one of theehambers, and an electrode mounted upon the diaphragm and vibratile therewith, the electrode having therein a restricted passageway coupling the two chambers. The passageway is of such construction as to permit free flow of air between the two chambers but to prevent passage of the carbon granules. Inasmuch as the housing is air-tight, the carbon granules are shielded from the atmosphere and aging eiects are minimized. Because interiorly Y carbon granules, those inone chamber serving"v to provide the variable resistance'current path for the transmitter and the granules in the ther i chamber providing a dissipative load to damp the' vibrations and suppress resonance peaks in the response characteristicof the transmitter.

In accordance with a further feature of this-' invention, in a device such -as described hereinabove wherein both chambers have carbon gran- 'ules therein, both masses of granules are utilized as variable resistance paths, thereby providing. push-pull operation'V inthe'v transmitter, andreducing modulation product and harmonie 'distortion. 'l

Ther inventionA and the above-.noted and other" features thereof will be uderstood more clearlii and fully from the following detailed descrip' tion wtih reference tothe accompanying drawing j in which Fig'. 1 is an' elevational view infsectionbra telephone transmitter illustrative of one embdiV mentof this invention;

Fig7 2 is a sect'inal viewto'a'n enlarged sc alef' of the vibratory granule ehatnber element in'cld-'f4 edin thedevic shown inFigl 1'; y

Fig. 2A' isJan explodedperspective"view of 'tlle' assembly illustrated in Fig.` 2,"

Fig. 3 is a graph illustrating the vfrel'tlue'ncy re-A sponse characteristic of a typicaldevic'of the construction shown in Fig. 1; and

Figs. 4 and 5' are sectional views, similar "toligV 2, illustrating otherembodiment of this" nvei4 tion. f

Supportedfrm thedaphragm and securely'- aiiixed 'to the center of the conical part 'f2 Atlfiereof, as by an adhesive indicated at f8 in FigZ, Ais a rigid spherical housing orcontainer composedof. two similar hemispherical parts ISA and l'lll'w advantageously ofy a metal, such as nilvar, having- .v a very low temperature coefiiecient of expansion.

is a thin metallic diaphragm which is sealed adjacent its periphery to the juxtaposed flanges on the hemispherical parts ISA and ISB thereby to form an air-tight enclosure. The sealing of the parts to one another may be effected by a suitable cement and joining of the parts and diaphragm under heat and pressure. One face of the diaphragm 20 which may be, for example of beryllium copper, has thereon a layer 2| of insulation for example, a coating of an enamel. Thus the diaphragm 20 is electrically integral with the hemispherical part ISA but is insulated from the hemispherical part ISB. A low resistance connection may be assured between the diaphragm 20 and part ISA by soldering the two together as indicated at 26 or, alternatively, by crimping the peripheral portion of the diaphragm 20 around and against the flange on the hemispherical part ISA.

Mounted upon and carried by the diaphragm 20 is a metallic stub-like electrode 22 which may 'be ailxed to the diaphragm by a nut 23 threaded thereon. The electrode 22 is provided with a restricted slot or bore 24, the purpose of which will appear presently;

The chamber bounded by the electrode 22, diaphragm 20 and hemispherical part ISB has therein a filling of comminuted resistance varying material 25, such as carbon granules. Advantageously, the inner wall of the part ISB and the surface of the electrode 22 in juxtaposition thereto have thereon a coating of gold to assure a permanent low resistance connection between the surfaces and the carbon granules.

As illustrated in Fig. 1, the hemispherical part ISB is connected electrically by a conductor 21 to a terminal 28 which is carried by an insulating plate 2S. The latter is heldY upon the frame II by a `clamping ring 30 threaded to the frame. This clamping ring may serve as a second terminal for the transmitter, leading to the electrode 22 over a. path which may be traced from the ring 30 over frame II to diaphragm I2, I3, I4, thence to the hemispherical part ISA and by way of the diaphragm 20 to the electrode 22.

In the operation of the dev-ice, sound waves incident upon the diaphragm I2, I3 and I4 through the apertures in the'protective cover I6 cause corresponding vibrations of the diaphragm. The housing ISA, ISB is actuated directly by and in accordance with the vibrations of the diaphragm. However, because of the compliant coupling between the electrode 22 and the housing IS by way of the diaphragm 20 and the 'difference in mass between the housing and the electrode 22. relative motion between the electrode and the housing obtains. Consequently, the resistance of the current path between the electrode 22 and the housing part ISB through the carbon granules 25 is modulated in accordance with the relative motion noted.

The frequency response of the device will be dependent, of course, upon the mechanical impedances of the vibratory system and these may be correlated in ways known in the art to produce a response covering any desired band of frequencies. For example, in one device, the parameters of the mechanical vibratory system may be correlated so that the device covers a frequency band of about 400 to 6,000 cycles in the manner illustratedinFig. 3.

To reduce resonance effects due to the chamber within the casing III, the frame or foundation rial 32 extends. 'Ihis material serves to lower the fundamental resonance frequency of the vibratory system including the diaphragm I2, I 3 and I4 and improve the response over the lower portion of the frequency range, say from about 400 to 1,000 cycles.

As is indicated in Fig. 3 and as is inherent in the structure disclosed, the vibratory system constituted by the electrode 22, the diaphragm 20 and the carbon granules 25, will have a resonance frequency which may be, for example, in the vicinity of about 2,000 cycles. The reponse peak due to this resonance frequency may be damped and substantially reduced by the construction illustrated in Fig. 4. In .this construction both the chambers within the-housing ISA, ISB, that is, the two hemispherical chambers on opposite sides of the diaphragm 20, have therein fillings of carbon granules indicated at 25 and 25A. The granular mass 25 in the construction illustrated in Fig. 4, as in that illustrated in Fig. 2 and described heretofore, provides the variable resistance current path between the electrode 22 and the hem'ispherical part ISB. The mass of granules 25A does not carry any of the transmitter current but acts as a dissipative load to damp the vibratory system including the diaphragm 20 and the electrode 22.

In another embodiment illustrated in Fig. 5, both the carbon masses 25 and 25A may be utilized as variable resistance elements. In this case, both faces of the diaphragm 20 have insulating coatings indicated at 2| and 2 IA thereon and two electrodes 22 and 22A both connected electrically to the diaphragm 20 are provided on opposite sides thereof. Each electrode together with the corresponding hemispherical part ISA or ISB, and the intervening carbon granules 25 or 25A, defines a variable resistance path separate from the other. The two paths may be associated electrically in known ways to provide push-pull operation.

It will be understood that in the constructions illustrated in Figs. 4 and 5, the electrode or elecapertures 3I over which acoustic damping matetrodes are provided with a restricted slot or bore similar to the bore 0r slot 24 illustrated in Fig. 2.

The slot or bore 24 allows free ow of air between the two chambers within the spherical housing ISA and ISB but is suiiciently small to prevent passage of the carbon granules therethrough. Because of the free flow of air permitted, it will be appreciated that automatic balancing of the air pressure forces acting upon opposite surfaces of the diaphragm 20 is realized. Thus, the vibratory characteristics of the inertia element are substantially unaffected by changes in the ambient pressure. Furthermore, inasmuch as, as has been pointed out heretofore, the housing parts I-SA and ISB advantageously are of 'a material having a very small temperature coefcient of expansion, the performance of the transmitter is substantially unaffected by variations in ambient temperature. Additionally, inasmuch as the housing is air-tight,v

aging of the carbon granules 25 or 25 and 25A is substantially reduced whereby the operating life of the telephone transmitter is extended.

Although specific embodiments of this invention have been shown and described, it will be understood that they art but illustrative and that various modications may be made therein without departing from the scope and spirit oi'` this invention.

What is claimed is:

1. A telephone transmitter comprising a housing, means mounting said housing for bodily vibration, means within said housing dividing the interior thereof into two chambers connected by a restricted passageway, said dividing means including an electrode and a flexible member mounting said electrode from said housing, said electrode extending into one of said chambers and the wall of said housing opposite said electrode being electrically conductive and insulated from said electrode, and comminuted resistance varying material in said one chamber, said restricted passageway being of such cross section as to permit the passage of air and to preclude the passage of said comminuted resistance varying material.

2'. A telephone transmitter in accordance with claim 1 comprising comminuted damping means for said flexible member in the other of said chambers.

3. A telephone transmitter comprising a housing, means mounting said housing for bodily vibration, means Within said housing dividing the interior thereof into two chambers connected by a restricted passageway, said dividing means including a pair of electrodes and a flexible member supporting said electrodes from said housing, each of said electrodes extending into a respective one of said chambers and being insulated from the wall of said housing in juxtaposition thereto, and comminuted resistance varying material in both of said chambers, said restricted passageway being of such cross section as to permit the passage of air and. to preclude the passage of said comminuted resistance varying material.

4. A telephone transmitter comprising a diaphragm, a container coupled to said diaphragm for vibration therewith, a second diaphragm within said container and dividing the interior thereof into two chambers, one face of Asaid diaphragm being electrically insulating and the Wall of said container opposite said one face being electrically conductive, an electrode mounted upon said second diaphragm and facing said wall, said electrode having a restricted passageway therein extending between said two chambers, and comminuted resistance varying material in the chamber between said wall and said one face.

5. A telephone transmitter comprising a diaphragm, a spherical metallic container mounted by said diaphragm, a second diaphragm extending across said container and dividing the interior thereof into a pair of chambers, carbon granules in one of said chambers, and an electrode mounted on said second diaphragm, contaeting said granules and insulated from the wall of said housing bounding said one chamber, said electrode having a restricted passageway therein extending between said pair of chambers.

6. A telephone transmitter comprising a diaphragm, a container coupled to said diaphragm for vibration therewith, said container including a pair of dished members having their open ends in juxtaposision, a second diaphragm eX- tending between said ends and affixed thereto, and defining with said members a pair of chambers, an electrode mounted by said second diaphragm and facing the base of one of said dished members, said one member being electrically conductive and insulated from said electrode, and carbon granules in the chamber between said one member and said second diaphragm.

7. A telephone transmitter in accordance with claim 6 comprising granular damping means for said second diaphragm in the other of said chambers.

8. A telephone transmitter comprising a .diaphragm, a container coupled to said diaphragm for vibration therewith, said container including a pair of dished members having their open ends in juxtaposition, a second diaphragm extending between said ends and aiiixed thereto, and defining with said members a pair of chambers, said diaphragm being insulated from said container, a pair of electrodes on opposite sides of said diaphragm and mounted thereby, and Iillings of carbon granules in both of said chambers.

9. A telephone transmitter comprising a diaphragm, a spherical air-tight container composed of two hemispherical nilvar members, a second diaphragm extending across said container and dividing the interior thereof into a pair of chambers, said second diaphragm being electrically conductive and insulated from one of said members, an electrode carried by said second diaphragm andfacing said one member, and a carbon granule iilling in the chamber between said electrode and said one member, said electrode having a restricted passageway therein dening an air coupling between said chambers.

10. A telephone transmitter comprising a metallic diaphragm having an insulating coating upon one face thereof, a pair of similar, aligned hemispherical members on opposite sides of said diaphragm and having their edges sealed in airtight relation to said diaphragm, the hemispherical member opposite said coating being electrically conductive and defining a carbon granule chamber with said diaphragm, an electrode mounted by said diaphragm, electrically connected thereto and extending into said chamber, said electrode having a restricted passageway therein dening an air leak between opposite sides of said diaphragm, and means for vibrating the diaphragm-hemispherical member assembly in accordance with sound waves.

l1. A telephone transmitter comprising a housing, means mounting said housing for bodily vibration, means within said housing dividing the interior thereof into two chambers connected by a restricted passageway, comminutedv resistance varying material in one of said chambers, the wall of said housing bounding said one chamber being electrically conductive, and an electrode in said one chamber, insulated from said wall and vibratile relative to said housing, said restricted passageway being of such cross section as to permit the passage of air and to preclude the passage of said comminuted resistance varying material.

HELMUTH ECKARDT.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 1,275,776 Skinderviken Aug. 13, 1918 1,354,229 Thompson Sept. 28, 1920 1,446,544 Bridgman Feb. 27, 1923 1,565,581 Moore Dec. 15, 1925 1,624,351 Moore Apr. 12, 1927 2,149,628 Pye Mar. 7, 1939 2,354,021 Horlacher July 18, 1944 2,485,920 Burroughs Feb. 10, 1948 

